This invention relates to an automatic document feeder for transporting documents placed on a document tray one sheet at a time onto a document table and, in particular, to such an automatic document feeder to be incorporated in an automatic two-side copying machine which can be operated selectably in either one-side copying mode or two-side copying mode.
An automatic document feeder which is made a part of a copying machine is a device for transporting documents placed on a document tray sequentially one sheet at a time onto a document table. In order to improve the operational efficiency of such a copying machine, it is necessary to reduce the time taken by the document feeder in exchanging document sheets. For this purpose, document feeders have been developed with a waiting position defined between the document table and the position where documents are stacked, a pre-feeding means being also provided such that, after a document is transported to the document table and while this document is being copied, the next document to be copied would be moved forward until its front edge comes to the waiting position. The basic idea of this method has been to reduce the distance to the document table which must be traveled by each document after the preceding document is copied and discharged.
If jamming takes place in a copying machine during its operation, the user must repeat the copying as many times as the number of the copies that were lost. Such operation is usually annoyingly complicated. If the jamming takes place while the second surfaces of the documents are being copied in the two-side copying mode of operation, not only the documents that have already been discharged into the discharge tray and the document which is then on the document table but also the document at the aforementioned waiting position to be fed next must be reset on the document tray. Since the next document to be fed is stopped in contact with the feeding means such as rollers, it must be pulled forcibly against the contact force of such feeding means in order to remove it from the waiting position.